diff --git a/src/builtin_argparse.cpp b/src/builtin_argparse.cpp
index dea5e1825..8ac8fa515 100644
--- a/src/builtin_argparse.cpp
+++ b/src/builtin_argparse.cpp
@@ -12,11 +12,11 @@
 #include <functional>
 #include <iostream>
 #include <iterator>
-#include <map>
 #include <memory>
 #include <sstream>
 #include <string>
 #include <type_traits>
+#include <unordered_map>
 #include <utility>
 #include <vector>
 
@@ -65,8 +65,8 @@ class argparse_cmd_opts_t {
     wcstring name = L"argparse";
     wcstring_list_t raw_exclusive_flags;
     wcstring_list_t argv;
-    std::map<wchar_t, option_spec_t *> options;
-    std::map<wcstring, wchar_t> long_to_short_flag;
+    std::unordered_map<wchar_t, option_spec_t *> options;
+    std::unordered_map<wcstring, wchar_t> long_to_short_flag;
     std::vector<std::vector<wchar_t>> exclusive_flag_sets;
 
     ~argparse_cmd_opts_t() {
diff --git a/src/builtin_string.cpp b/src/builtin_string.cpp
index 03dfa1f07..a1e199ac0 100644
--- a/src/builtin_string.cpp
+++ b/src/builtin_string.cpp
@@ -17,9 +17,9 @@
 #include <algorithm>
 #include <cwctype>
 #include <iterator>
-#include <map>
 #include <memory>
 #include <string>
+#include <unordered_map>
 #include <utility>
 #include <vector>
 
@@ -387,7 +387,7 @@ static const struct woption long_options[] = {{L"all", no_argument, NULL, 'a'},
                                               {L"style", required_argument, NULL, 1},
                                               {NULL, 0, NULL, 0}};
 
-static std::map<char, decltype(*handle_flag_N)> flag_to_function = {
+static std::unordered_map<char, decltype(*handle_flag_N)> flag_to_function = {
     {'N', handle_flag_N}, {'a', handle_flag_a}, {'c', handle_flag_c}, {'e', handle_flag_e},
     {'f', handle_flag_f}, {'i', handle_flag_i}, {'l', handle_flag_l}, {'m', handle_flag_m},
     {'n', handle_flag_n}, {'q', handle_flag_q}, {'r', handle_flag_r}, {'s', handle_flag_s},
diff --git a/src/common.h b/src/common.h
index 3ef074bd0..3846e32e2 100644
--- a/src/common.h
+++ b/src/common.h
@@ -832,3 +832,19 @@ enum {
 #endif
 
 #endif
+
+// Custom hash function used by unordered_map/unordered_set when key is const
+#ifndef CONST_WCSTRING_HASH
+#define CONST_WCSTRING_HASH 1
+namespace std {
+  template <>
+  struct hash<const wcstring>
+  {
+    std::size_t operator()(const wcstring& w) const
+    {
+        std::hash<wcstring> hasher;
+        return hasher((wcstring) w);
+    }
+  };
+}
+#endif
diff --git a/src/complete.cpp b/src/complete.cpp
index d570c4ce8..48c54b973 100644
--- a/src/complete.cpp
+++ b/src/complete.cpp
@@ -16,11 +16,11 @@
 #include <functional>
 #include <iterator>
 #include <list>
-#include <map>
 #include <memory>
 #include <set>
 #include <string>
 #include <type_traits>
+#include <unordered_map>
 #include <unordered_set>
 #include <utility>
 
@@ -292,7 +292,7 @@ class completer_t {
 
     /// Table of completions conditions that have already been tested and the corresponding test
     /// results.
-    typedef std::map<wcstring, bool> condition_cache_t;
+    typedef std::unordered_map<wcstring, bool> condition_cache_t;
     condition_cache_t condition_cache;
 
     enum complete_type_t { COMPLETE_DEFAULT, COMPLETE_AUTOSUGGEST };
@@ -596,7 +596,7 @@ void completer_t::complete_cmd_desc(const wcstring &str) {
     wcstring lookup_cmd(L"__fish_describe_command ");
     lookup_cmd.append(escape_string(cmd_start, 1));
 
-    std::map<wcstring, wcstring> lookup;
+    std::unordered_map<wcstring, wcstring> lookup;
 
     // First locate a list of possible descriptions using a single call to apropos or a direct
     // search if we know the location of the whatis database. This can take some time on slower
@@ -634,7 +634,7 @@ void completer_t::complete_cmd_desc(const wcstring &str) {
             const wcstring &el = completion.completion;
             if (el.empty()) continue;
 
-            std::map<wcstring, wcstring>::iterator new_desc_iter = lookup.find(el);
+            auto new_desc_iter = lookup.find(el);
             if (new_desc_iter != lookup.end()) completion.description = new_desc_iter->second;
         }
     }
@@ -1553,7 +1553,7 @@ wcstring complete_print() {
 
 /// Completion "wrapper" support. The map goes from wrapping-command to wrapped-command-list.
 static std::mutex wrapper_lock;
-typedef std::map<wcstring, wcstring_list_t> wrapper_map_t;
+typedef std::unordered_map<wcstring, wcstring_list_t> wrapper_map_t;
 static wrapper_map_t &wrap_map() {
     ASSERT_IS_LOCKED(wrapper_lock);
     // A pointer is a little more efficient than an object as a static because we can elide the
diff --git a/src/env.cpp b/src/env.cpp
index 2b183d6d7..0030e3aa0 100644
--- a/src/env.cpp
+++ b/src/env.cpp
@@ -30,9 +30,9 @@
 #endif
 
 #include <algorithm>
-#include <map>
 #include <set>
 #include <type_traits>
+#include <unordered_map>
 #include <utility>
 #include <vector>
 
@@ -85,7 +85,7 @@ bool term_has_xn = false;
 /// found in `TERMINFO_DIRS` we don't to call `handle_curses()` before we've imported the latter.
 static bool env_initialized = false;
 
-typedef std::map<const wcstring, void (*)(const wcstring &, const wcstring &)> var_dispatch_table_t;
+typedef std::unordered_map<const wcstring, void (*)(const wcstring &, const wcstring &)> var_dispatch_table_t;
 var_dispatch_table_t var_dispatch_table;
 
 /// List of all locale environment variable names that might trigger (re)initializing the locale
@@ -1596,7 +1596,7 @@ env_var_t env_vars_snapshot_t::get(const wcstring &key) const {
     if (this->is_current()) {
         return env_get(key);
     }
-    std::map<wcstring, env_var_t>::const_iterator iter = vars.find(key);
+    auto iter = vars.find(key);
     return iter == vars.end() ? missing_var : env_var_t(iter->second);
 }
 
diff --git a/src/expand.cpp b/src/expand.cpp
index 50168222f..733d11422 100644
--- a/src/expand.cpp
+++ b/src/expand.cpp
@@ -27,9 +27,9 @@
 
 #include <algorithm>
 #include <functional>
-#include <map>
 #include <memory>  // IWYU pragma: keep
 #include <type_traits>
+#include <unordered_map>
 #include <utility>
 #include <vector>
 
@@ -1566,7 +1566,7 @@ bool fish_xdm_login_hack_hack_hack_hack(std::vector<std::string> *cmds, int argc
     return result;
 }
 
-std::map<const wcstring, const wcstring> abbreviations;
+std::unordered_map<const wcstring, const wcstring> abbreviations;
 void update_abbr_cache(const wchar_t *op, const wcstring &varname) {
     wcstring abbr;
     if (!unescape_string(varname.substr(wcslen(L"_fish_abbr_")), &abbr, 0, STRING_STYLE_VAR)) {
diff --git a/src/function.cpp b/src/function.cpp
index 04dd5dfb9..6571f3081 100644
--- a/src/function.cpp
+++ b/src/function.cpp
@@ -14,6 +14,7 @@
 #include <memory>
 #include <set>
 #include <string>
+#include <unordered_map>
 #include <utility>
 
 #include "autoload.h"
@@ -28,7 +29,7 @@
 #include "wutil.h"  // IWYU pragma: keep
 
 /// Table containing all functions.
-typedef std::map<wcstring, function_info_t> function_map_t;
+typedef std::unordered_map<wcstring, function_info_t> function_map_t;
 static function_map_t loaded_functions;
 
 /// Functions that shouldn't be autoloaded (anymore).
diff --git a/src/highlight.cpp b/src/highlight.cpp
index adefd969b..bbd3abac9 100644
--- a/src/highlight.cpp
+++ b/src/highlight.cpp
@@ -9,11 +9,11 @@
 #include <wchar.h>
 
 #include <algorithm>
-#include <map>
 #include <memory>
 #include <set>
 #include <string>
 #include <type_traits>
+#include <unordered_map>
 #include <utility>
 
 #include "builtin.h"
@@ -67,7 +67,7 @@ static const wchar_t *const highlight_var[] = {L"fish_color_normal",
 /// Returns:
 ///     false: the filesystem is not case insensitive
 ///     true: the file system is case insensitive
-typedef std::map<wcstring, bool> case_sensitivity_cache_t;
+typedef std::unordered_map<wcstring, bool> case_sensitivity_cache_t;
 bool fs_is_case_insensitive(const wcstring &path, int fd,
                             case_sensitivity_cache_t &case_sensitivity_cache) {
     bool result = false;
diff --git a/src/lru.h b/src/lru.h
index c5a9bb994..39b4a683d 100644
--- a/src/lru.h
+++ b/src/lru.h
@@ -4,7 +4,7 @@
 
 #include <wchar.h>
 
-#include <map>
+#include <unordered_map>
 
 #include "common.h"
 
@@ -22,8 +22,6 @@
 template <class DERIVED, class CONTENTS>
 class lru_cache_t {
     struct lru_node_t;
-    typedef typename std::map<wcstring, lru_node_t>::iterator node_iter_t;
-
     struct lru_link_t {
         // Our doubly linked list
         // The base class is used for the mouth only
@@ -47,6 +45,8 @@ class lru_cache_t {
         explicit lru_node_t(const CONTENTS &v) : value(std::move(v)) {}
     };
 
+    typedef typename std::unordered_map<wcstring, lru_node_t>::iterator node_iter_t;
+
     // Max node count. This may be (transiently) exceeded by add_node_without_eviction, which is
     // used from background threads.
     const size_t max_node_count;
@@ -54,7 +54,7 @@ class lru_cache_t {
     // All of our nodes
     // Note that our linked list contains pointers to these nodes in the map
     // We are dependent on the iterator-noninvalidation guarantees of std::map
-    std::map<wcstring, lru_node_t> node_map;
+    std::unordered_map<wcstring, lru_node_t> node_map;
 
     // Head of the linked list
     // The list is circular!
diff --git a/src/pager.cpp b/src/pager.cpp
index 2dbc95d93..c53e928fe 100644
--- a/src/pager.cpp
+++ b/src/pager.cpp
@@ -6,8 +6,8 @@
 #include <wctype.h>
 
 #include <algorithm>
-#include <map>
 #include <numeric>
+#include <unordered_map>
 #include <vector>
 
 #include "common.h"
@@ -267,7 +267,7 @@ static void mangle_1_completion_description(wcstring *str) {
 static void join_completions(comp_info_list_t *comps) {
     // A map from description to index in the completion list of the element with that description.
     // The indexes are stored +1.
-    std::map<wcstring, size_t> desc_table;
+    std::unordered_map<wcstring, size_t> desc_table;
 
     // Note that we mutate the completion list as we go, so the size changes.
     for (size_t i = 0; i < comps->size(); i++) {
diff --git a/src/screen.h b/src/screen.h
index f7960a6a0..c06ffaf12 100644
--- a/src/screen.h
+++ b/src/screen.h
@@ -16,9 +16,9 @@
 
 #include <algorithm>
 #include <cstddef>
-#include <map>
 #include <memory>
 #include <set>
+#include <unordered_map>
 #include <vector>
 
 #include "common.h"
@@ -214,7 +214,7 @@ class cached_esc_sequences_t {
     // sequence lengths we've actually cached to avoid checking for matches of lengths we know are
     // not in our cache.
     std::vector<size_t> lengths;
-    std::map<size_t, size_t> lengths_match_count;
+    std::unordered_map<size_t, size_t> lengths_match_count;
     size_t cache_hits;
 
    public:
diff --git a/src/wutil.cpp b/src/wutil.cpp
index 928557c00..14b63875c 100644
--- a/src/wutil.cpp
+++ b/src/wutil.cpp
@@ -17,8 +17,8 @@
 #include <wchar.h>
 #include <wctype.h>
 
-#include <map>
 #include <string>
+#include <unordered_map>
 
 #include "common.h"
 #include "fallback.h"  // IWYU pragma: keep
@@ -38,7 +38,7 @@ const file_id_t kInvalidFileID = {(dev_t)-1LL, (ino_t)-1LL, (uint64_t)-1LL, -1,
 #endif
 
 /// Map used as cache by wgettext.
-static owning_lock<std::map<wcstring, wcstring>> wgettext_map;
+static owning_lock<std::unordered_map<wcstring, wcstring>> wgettext_map;
 
 bool wreaddir_resolving(DIR *dir, const wcstring &dir_path, wcstring &out_name, bool *out_is_dir) {
     struct dirent d;